1. Field of the Invention
The present invention relates to a plasma process apparatus with in situ monitoring, a method for monitoring using the apparatus, and a method for cleaning a chamber used in the apparatus. More particularly, the present invention relates to in situ monitoring a plasma chamber using a sampling manifold connected to the chamber and a gas analyzer connected to the manifold, and includes a method for in situ monitoring a plasma process and a method for cleaning the plasma chamber after etching. In addition, the present invention relates to an optimized in situ cleaning method for removing residues inside a plasma chamber after etching polysilicon.
2. Description of the Related Art
Generally, semiconductor device fabrication processes are carried out in processing chambers in which specific processing conditions, such as temperature and pressure, are preset and processing environments are created. In particular, a plasma process, such as a plasma etching process and a plasma enhanced chemical vapor deposition (PECVD) process, generates many by-products. These by-products react with gas, photoresist, or other materials present inside the processing chamber to create polymer materials. The polymer becomes attached to the wafer surface and the inside surfaces of the processing chamber, causing the processing parameters to deviate from the preset values, and generating particles. Particles cause wafer defects which result in a decrease in the productive yield of a semiconductor fabrication facility.
In order to reduce defects, preventive maintenance (PM) for the processing chamber is carried out on a certain schedule. Because the equipment can not be operated during PM, productivity is also reduced by frequent PM.
FIG. 1 shows the PM process for the conventional processing chamber. Equipment for a specific process of semiconductor fabrication, with a chamber requiring PM, is removed from operation, is powered off, has its vacuum released, and is allowed to cool down. When the processing chamber is sufficiently cooled down, the components of the processing chamber are disassembled. In the case of chambers used in plasma processes, the surfaces of each of the disassembled components are wet-etched to remove the by-products of plasma processing. The wet-etch normally uses chemicals in the hydrogen fluoride (HF) series in order to remove the polysilicon film or silicon nitride film. Then, after re-assembling the components, a vacuum pump is again operated to reestablish a vacuum, the power is turned on, and the equipment is brought on line. Test wafers are then loaded into the processing chamber of the equipment, and an aging process ensues. After aging, the test wafers are examined during Process Recertification, in order to check whether the processing chamber is ready for operational use.
However, the PM method described has some drawbacks. The method is expensive, wastes energy and takes a long time (over 24 hours).
In order to overcome the time problem, a plasma etch can be carried out using nitrogen trifluoride (NF.sub.3), or carbon tetrafluoride (CF.sub.4) instead of the wet etch. Alternatively, Thermal Shock Technology is employed to remove, by means of thermal stress, the films formed inside the chamber. In another alternative, a dry etch is performed using chlorine trifluoride (ClF.sub.3), or bromine pentafluoride (BrF.sub.5). Even with this alternative, the removal, the disassembly and the assembly are still required thereby resulting in the same economic losses and power waste.
In situ cleaning, without disassembly and assembly, for the processing chamber using dry etch gas has been introduced. However, it is difficult to measure the cleaning reaction precisely as it is being carried out and to determine the most efficient cleaning conditions. Thus, proper utilization of the in situ cleaning function is difficult, and optical utilization is unlikely.